Starter for electric motors



March 18, 1947. 5, 5M|TH 2,417,710

STARTER FOR ELECTRIC MOTORS Filed Feb. 2, 1944 A 1- Hz "F2 A2 Al as 175CB 2 FZ AZ Al F'i Zmomto: I F 16. 5 ml EDWARDR SMITH E] I W I I,

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Patented Mar. 1e,- 1e47 STARTER FOR ELECTRIC MbTORS Edward P. Smith,Mansfield, Ohio, asslgnor to The Ohio Brass Company, Mansfield, 01110, acorporation of New Jersey Application February 2, 1944, Serial No;521,003

My invention relates to starters for electric motors and has particularreference to starters oi the type employing a starting resistance.

One object of my invention is to provide a mo-- tor starter employing astarting resistance and a shorting switch to shunt out the resistanceafter a lapse of time.

Another object of my invention is to provide a means which will insurethe shunting out of the starting resistance and a completion of thestarting cycle.

Another object of my invention is to provide a motor starter in whichthe acceleration of the motor armature is controlled through variationof armature voltage or armature current or both including means toeffect completion of the timing cycle under adverse starting conditions.

Another object of my invention is to provide a motor starter havingthermally controlled means to increase the voltage applied to mechanismfor shunting out the starting resistance after a period of time.

Another object of my invention is to provide an automatic starterincluding a resistance shunting switch with an operating coil includingmeans to automatically control the energization of the coil after a timelag.

Another object of my invention is to provide an automatic starter inwhich the operating coil for the resistance shunting switch is in serieswith a resistor in which the resistance decreases as the temperature ofthe resistor increases, to bring the coil up to "its operating strengthafter a time lapse.

Another object of my invention is to provide an automatic motor starterhaving a shorting switch for the starting resistance and with a holdoutcoil in series with thestarting resistance and an operating coil for theswitch provided with means to increase the-operating strength of thecoilto overcome the holdout coil after a lapse of time.

Still another object of my invention is to provide a motor starterhaving a control resistor with a negativecoeificient of resistance andmeans to heat the same whereby its resistance is reduced accordingly.

Other and further objects of my invention, as well as advantages anduses, will become appar: ent as the description and claims are read andupon examination of the accompanying drawings, in which- Fig. 1 is aschematic diagram of one form of my invention.

27 Claims.- (01. 172-288) Fig. 2 is a line diagram 01' a modification cFig. 1. Fig. 3 is a schematic diagram of another to oimy invention.

Fig. 4 is a line diagram 0! a modification of Fig. 3.

Fig. 5 is a schematic. diagram of still another form of my invention.

Fig. 6 is a, line diagram oi a modification oi Fig. 5.

All three forms of my invention shown by Figs. 1, 3 and 5 are relatedtypes oi direct current motor starters and omitting certain features,which are new and novel with me, they are in general forms familiar tothose skilled in the art.

However, under conditions of abnormal overload or low main line voltagesuch prior art starters are not dependable as the starting resistance isnot necessarily shunted out and the starting cycle is not complete,thereby causing the starting resistance to remain as a part of thestarting circuit, resulting in either damage to the motor starter orinefficient operation of the motor.

During the starting cycle,,the acceleration of the motor speed may bevery slow or acceleration may not take place at all if the load-is toogreat or the line voltage low in which case the starting current willdecrease very slowly or remain constant and not decrease to normal as itshould, and at the same time the counter E. M. F. of the motor armaturewill not increase as it should under normal starting conditions.

I depend upon the decrease in the starting current and the increase inthe counter E. M. F. of the motor armature to control the normaloperation of the shunting switch and upon auxiliary means associatedwith the shunting switch to effect operation thereof under adversestarting conditions, to shunt out the starting resistance;

The main object of my improvement is to provide means which will insurethe completion of the starting cycle without materially complicating thestarting circuit.

In the embodiment of my invention, disclosed schematically in Figs. 1and 2, A designates the armature of a direct current motor, theterminals of which are connected to posts Al and A2 of the starter. Themotor has a field winding W having its terminals connected to. the postsFl and F2 of the starter.

Current is supplied to the starter and motor I through the supply line Iand return conductor 2. The current from the supply line I is controlledby a. main or disconnecting switch DS which closes the circuit to theconductor 3 and which includes the fuse F and is connected to thecircuit breaker CB having contacts 4 and 5. The contact is operated bythe armature I actuated by the solenoid or electromagnet coll M.

The contacts 4 and 5 are normally held open as by a spring or gravitywhen the solenoid M is not energized.

The armature 6 is connected to the starting resistance SR by theconductor 1 and to one terminal 8 of a shorting switch SS by conductor9. The other terminal or contact ID of the shorting switch SS isoperated by the armature H, actuated by the solenoid or electromagnetcoil C.

The other terminal of the starting resistance SR is connected to thepost Al by the conductor l2 and to the armature II by the conductor I3.

The coil M is energized while the control switch CS- is closed thusconnecting the coil M to the conductor 3 and to the conductor 2 throughthe conductor H. The switch CS is usually of the push-button type. Whenthe coil M is de-energized the contacts 4 and 5 are open. The fieldwinding W is connected to the posts Fl and F2 which in turn areconnected to the power lines 1 and 2 by the conductors l5 and I8respectively.

One terminal of the coil C is connected to conductor H and the otherterminal is connected to conductor l3 through an interposed controlresistor CR. It will be noted that the coil C in series with resistor CRis thus connected across the terminals of the motor armature A, and theenergization of the coil C therefore depends upon the operation oracceleration of the motor in starting, in other words the closing of theshorting switch SS and the cutting out of the starting resistance SRdepends upon the counter E. M. F. generated by the motor.

Closing the control switch CS after closing the disconnecting switch DS,energizes the coil M which in turn closes the circuit breaker CBtherefore establishing a circuit including conductor i, switch DS, fuseF, circuit breaker CB, conductor 2, starting resistance SR, conductorl2, armature A and conductor 2.

Most resistance elements have a positive temperature coefficient ofresistance, that is the resistance increases as the temperature of theelement increases but I use a resistance element CR having a negativetemperature coefllcient of resistance, that is for a given E. M. F.across its rminals the resistance of the element decreases as itstemperature rises thereby allowing more current to flow as thetemperature of the element CR increases.

Such a resistance element may be one of carbonaceous material or ofcarbonaceous material combined with other materials whereby thecharacteristics of the element may be made to meet requirements.

I am unable to say just what the composition of such an element is orshould be to meet given requirements or what treatment is applied to thematerial to produce such elements having a negative temperaturecoefficient of resistance as this is within the knowledge of themanufacturer.

The characteristics of such elements may be greatly varied by a chang inthe composition and treatment but such elements are obtainable on themarket from certain manufacturers of carbon products. Thecharacteristics of a CR element must be such as to harmonize with theother elements of the starter with which it is used and with thecharacteristics of the motor and therefore I am unable to give anydefinite 4 characteristics which will meet all the various conditions.

As stated before, and still referring to Figs. 1 and 2, the coil C andcontrol resistor CR are connected in series and across the motorarmature A and the energization therefore of the coil C depends upon thecounter E. M. F. generated by the motor and upon the performance of thecontrol resistor CR.

The coil C and control resistor CR are so designed and proportioned asto permit an elapse of time after the motor starts before the shortingswitch SS operates to cut out the starting resistance SR but laterinsures the completion of the starting cycle if normal predeterminedconditions of operation of the motor in starting are not attained:

The coil C and resistor CR are designedand proportioned to functionproperly with the motor with which the starter is to he used and is suchthat when the armature voltage, increasing as the armature accelerates,reaches a predetermined value under normal starting, say one-half thatof the supply voltage, the shorting switch S8 will close thus cuttingout the starting resistance SR and thereby completing the runningcircuit.

The cold resistance of the control resistor CR may be made substantiallythat of the coil C.

The wattage rating of the control resistor CR is such that the currentflowing therethrough will cause the resistor to gradually heat andsimultaneously the resistance will decrease until it reaches its normaloperating temperature at which it resistance may be about 6 that of itscold resistance.

Under normal starting operation, in which the load on the motor is nottoo high, the speed oi the motor increases gradually until the E. M. F.of the motor reaches a predetermined value at which the switch SScloses; in this case the effect of the control resistor CR is of minorimportance. As the motor continues to build up speed the armature ormotor operating current will gradually decrease and the counter E. M. F.of the motor will gradually increase, but if the load on the motor istoo great, it will prevent the arms.- ture speed accelerating properlyand therefore prevent the counter E. M. F., reaching a. value suflicientto cause the necessary energlzation oi the coil C and to closetheshorting switch S8 at the adjusted value thereof.

In this latter case, as the current continues to flow through thecontrol resistor CR, the resistor will gradually increase in temperatureand simultaneously its resistance will decrease, thus allowing anincreasing flow of current through the coil C until after a lapse oftime the current flow through the coil C is sufilcient to energize thecoil to close the shorting switch SS and cut out the starting resistanceand thus subject the motor directly to the full line voltage.

If in the latter case the speed of the motor should simultaneouslyincrease somewhat with th heating of the control resistor CR this willalso assist in assuring a closing of the shorting switch SS at anearlier period as the current flow through the coil C will increase thatmuch faster.

From the above it will be evident that the control resistor CR willautomatically permit an increasing amount of current to how through thecoil C if the acceleration of the motor armature is abnormally slowuntil a condition is reached wherein the current flow through the coil Cis sufficient to operate the shorting switch SS and this is true eventhough the counter E. M. F. of

the motor does not increase.

If desired, a. shorting switch a: operated by the armature ll may beused whereby the control resistor CR is short-circuited while the switchSS is closed during normal operation of the motor. This permits theoperation of the control ,resistor CR at atemperatur above that which'means of heating\the resistor, depending upon the design. In Fig. 2 theswitch a: is omitted butmay be included if desired.

In Fig. 3 and its modification shown in Fig. 4, the arrangement isthesame as in Figs. 1 and 2 respectively exceptior the addition of ahold-out solenoid or electromagnet coil HO and the omission of theswitch a: in Fig. 4, therefore I have designated the other partsoi thecircuits of Figs. 3 and 4 by the same characters as used in Fig. 1 and 2and in Figs. 5 and 6 forthe same reasons. In Fig. 4, the resistor CR issupplied with an auxiliary heater H.

The hold-out coil HC is connected in series with the starting resistanceSR and acts upon the armature to hold the shorting switch SS openagainst the pull of the coil C which is simultaneously energized. Itwill be noted that the coil C and the resistor CR are connected toconductors 2 and l and therefore directly across line, hence areenergized independently of the counter E. F. of the motor.

When the switches D8, CS and CB have been closed the motor will startaccelerating with the -starting resistance SR in series therewith andwith the coil HC, therefore the current in the starting circuit willenergize the hold-out coil H0. The construction and relation of theparts of switch SS are such that its coil HC controls and holds theswitch SS open until such time as the acceleration of the armature A hasreached a speed at which the current therethrough has graduallydecreased thereby gradually de-ener-' gizing the coil I-IC until thecurrent has reached a predetermined value of possibly 125 percent of therated full load current at which point the energization of coil C eitherremains constant or has increased due to resistor CR and become superiorto that of coil HC, at which time the coil C acting upon the armature itcloses the short' ing switch SS. throwing the motor directly upon fullline voltage.

Since the coil C and resistor CR are connected to a source of constantvoltage, any variation in the energization of the coil C is due tovariation of the resistance of resistor CR.

The combined operation of the coil C and control resistance CR in Figs.3 and 4 is the same as explained above in the case of Fig. i should theacceleration of the motor be unduly delayed as in case of abnormalstarting.

The control resistor CR in Figs. 3 and 4 may he short-circuited by theswitch or operated by the armature H, as in the case of Fig. 1.

In the starter shown in Figs. 5 and 6 which are similar to the startersof Figs. 3 and 4 respectively there is a differential action betweencoil 0 and the hold-out coil HC, the acceleration of the armatureaffecting the energization of both coils in that as the acceleration ofthe armature increases, the starting current which is normally high,decreases, thereby decreasing the energization of coil HC and at thesame time the counter E. M. F. of the armature increases, therebyincreasing the energization of the coil C.

The coil C and its control resistor CR in the case of Figs. 5 and 6 areconnected across the armature A and therefore the energization of coil Cand the operation of the resistor CR are affected by the counter E. M.F. of the armature, while in the case of Figs. 3 and 4 the coil C andresistor CR are subject to a constant line voltage.

In case of Figs. 5 and 6, in starting under an overload or a low linevoltage in which case the acceleration of the motor is very slow orabsent, control resistor CR tends to heat due to the prolonged iiow ofcurrent therethrough and its resistance drops thus permitting morecurrent to flow through the coil C as a result of the counter E. M. F.of the armature which may remain constant or increase slightly until theenergization of the coil C' is superior to that of coil HC, whereuponthe switch SS is closed and the starting resistance shunted out. Thecombined action of the coil C and of the control resistor CR is the sameas in Fig. 1.

If in Figs. 5 and 6 the acceleration of the motor is continuous afterthe closing of the control switch CS, then the energization of the coilHC will gradually decrease and the energization of the coil C willgradually increase until the pull of coil C becomes superior to that ofcoil I-IC thereby closing switch SS without the control resistor heatingand playing much part in the operation.

In Fig. 6 the resistor CR is shown adjacent the starting resistance SRwhich may become very hot and the radiated-heat acts as auxiliaryheating means for the resistor.

In Figs. 5 and 6 the use of switch :1: operated by the armature 6 isoptional as. in the other cases.

In Figs. 1, 2, 5 and 6 the energization of the coil C and thefunctioning of the control resistor CR depends upon the counter E. M. F.of the armature which under normal startin 'conditions will graduallyincrease until the current flowing through coil C energizes the coilsufiiciently to close the switch SS. I

If, however, there is a prolonged period of starting as in the case ofan overload or low line voltage, then the counter E. M. F. of thearmature may remain constant or increase very slowly, resulting in theheating, assisted by the auxiliary means, of the control resistor CR,the resistance of which decreases, permitting more current to flowthrough the coil C until its energization is sufiicient to operate theswitch SS. With a given counter E. M. F. of the motor armature, thevoltage drop'across the coil C will increase as the resistance of thecontrol CR decreases.

As before stated, in the case of Figs. 3 and 4 the coil C and itscontrol resistor CR are connected directly across the line and aretherefore subject to full line voltage which is con stant and are notdependent upon the variable counter E. M. F. of the armature, thereforeany variation in the energization of coil C is due to variation of theresistance of resistor CR.

. i 7 ergization of coil C will-be superior-to that of coil HC due tothe armature current decreasing as the armature speed increases untilthe pull of coil HC is weaker than that 01' coil C, whereupon the switchSS will close.

There is an advantage in the use of my improved control element CR overthat of the prior art in that it is simpler, has no movin parts,

nothing to get out of adjustment, functioning entirely different fromdevices of the prior art for the same purpose in motor starters, viz.,to control the operation of the shunting switch for the startingresistance and last but not least the control element CR is quiteuniform in operation especially when inclosed and unaffected by aircurrents and temperature changes from without.

There might be conditions when it would be desirable to cut-out only apart of the starting resistance, in which case the contact 8 would beconnected to the starting resistance SR at some point between theterminals of the starting resistance and not connected to the conductor1, as will be evident to those skilled in the art.

While I prefer to use a resistor CR which is self-heating, that is bythe current passing therethrough and through the coil C, under someconditions the resistor CR may have such characteristics as not to beself-heating or not sumciently self-heating and in that case, heatingmust result indirectly from an auxiliary source a H or SR. The heater Hmay be applied to Fig, 3 in the same manner as in Fig. 4 in which casethe heater will be shorted when resistor CR is shorted.

If desired the auxiliary heater shown in Figs.

' 1 and 2 may be connected directly across the starting resistance.

The armature H in each starter is held in its open position by gravityor a light spring when coils C and K are not energized.

The spring a in Figs. 1, 4 and 6 are of the compression type and inFigs. 2, 3 and are of the tension type and may be used to adjust thetime of closing of the shunting switch SS.

Starters have been produced employing a closing coil and a lock-out coilacting upon a shorting switch with a thermal or bi-metal switch to shortthe lock-out coil after a lapse of time, but I employ entirely diiierentmeans acting upon th closing coil whereby the starter shunts out thestarting resistance under normal starting of the motor and insures theshunting of the starting resistance under abnormal starting conditions.

In Figs. 1 and 5 the resistors are entirely selfheating and dependentupon a variable source of E. M. F. Therefore the time lag is not asfixed as in the case of Fig. 3 where the control circuit is connecteddirectly to the supply lines where the E. M. F. is constant.

In Fig. 3 there is a definite maximum lapse oi time due to the linevoltage and the characteristics of the coil C being constant and theresistance of the resistor CR becoming constant when the temperature ofthe resistor reaches a predetermined value. With proper selection anduse of the resistor CR, the time lag in which the shunting switch SS maybe made to close against resistance to closing may be brought intoreasonably close limits desired within the said maximum definite lapseof time;

If the resistance to closing i v the coil K0, the pull of this coil willdecrease as the motor speeds 8 up until its pull is just overcome by thePull 0! the coil C and the switch 88 will close.

That which is required as new and useful and which is sought to beprotected by Letters Patent 01! the United States is as follows:

1. In combination, a motor armature, a starting resistance in serieswith said armature, operable means for effectively eliminating saidresistance from the circuit oi. said armature when the counter E. M. F.of the motor armature attains a predetermined value, and supplementalmeans having a time lag in its operation thus insuring the functioningof the operable means and the elimination of said resistance from saidarmature circuit in case said counter E. M. F. of the motor armaturefails to attain said predetermined value within the time lag period 01'said sup- .plemental means, the said supplemental means comprising aresistance having a negative coeflicient of resistance in series withsaid operable means whereby the operable means becomes eifective at alower counter E. M. F. of the motor than said predetermined value.

2. The combination with a motor armature of a starter resistance inseries with said armature, a shunting switch for said starterresistance, a coil connected across said armature for closing saidswitch when the counter E. M. F. 0! the armature reaches a predeterminedvalue. and supplemental means having a time lag in its operation thusinsuring the functioning of the coil to close the switch and effectivelyeliminate said resistance from the said armature circuit in case thecounter E. M. F. of the armature fails to attain said predeterminedvalues within the time lag period of said supplemental means, the saidsupplemental means comprising a resistance having a negative coefficientof resistance in series with said coil whereby the coil becomesefiective at a lower counter E. M. F. of the armature than the saidpredetermined value to close the switch.

3. The combination with a motor having an armature and a field winding,of a starting resistance in series with the armature, a switch forshunting out the starting resistance, a solenoid for closing the switch,control means connected in series with the said solenoid, the saidsolenoid and control means connected across the armature whereby theyare subject to the counter E. M. F. of the armature to close the switchwhen the counter E. M. F. of the armature reaches a predetermined valueunder either a, normal starting condition or under a lower counter E. M.I". of the armature providing the armature fails to attain saidpredetermined counter E. M. F. after a lapse of time in starting, thesaid control means comprising a resistance having a negative temperaturecoefficient of resistance.

4. In an automatic starter for electric motors having an armature, thecombination of a starting resistance arranged to be connected in serieswith the armature, means for automatically shunting out the startingresistance, the said means actuated by means controlled by the counterE. M. F. of the armature to shunt the starting resistance when thecounter E. M. F, of the armature increases to a predetermined value andto shunt the starting resistance after a lapse of time regardless of thefailure of the counter E. M. F. of the armature to increase.

5. In an automatic starter for electric motors having an armature, thecombination of a starting resistance arranged to be connected in serieswith the armature, means for automatically starting resistance arrangedto be connected in series with the armature, a shunting out switchprovided with an operating coil to close the switch after a lapse oftime and the current through the operating coil has reached a value tosumciently energize the coil due to the counter E. M. F. of the armaturehaving reached a predetermined value and control means associated withthe coil and arranged to gradually increase the current through the coilwhen the counter E. M. F. of the armature fails to reach a predeterminedvalue.

'7. An automatic starter for electric motors comprising a startingresistance, means including an operating coll for shunting out saidresistance after a lapse of time the energization of said coil foroperating the shunting out means depending upon the counter E. M. F. ofthe motor increasing to a predetermined value and means in series withsaid operating coil to gradually effect an increase of current flowthrough said shunting out coil to energize the coil sufficiently tooperate the shunting out means when the counter E. M. F. of the motorfails to increase sufiiciently.

8. An automatic starter for an electric motor having an armaturecomprising, a starting resistance, switch means for shunting out thestarting resistance, the said switch means including current responsiveoperating means, and control means associated with the operating meansthe control means increases due to the current, flow through the coiland control means, the said coil operating to actuate the shuntingswitch if and when the speed of the motor reaches a predetermined value,the control means operating to effect sufficient energ zation of thecoil after a lapse of time to actuate the shunting out switch regardlessof the starting condition of the motor.

10. An automatic starter foran electric motor comprising, a startingresistance, means for shorting the starting resistance, the saidshorting means including current responsive means and its connections toa source of power to actuate I the shorting means to its shortingposition after a time lag and to maintain said position, the currentresponsive means including control means so constructed and so relatedto the current responsive means as to effect. a decrease in theresistance of the circuit of the current responsive means whereby thecurrent through the current responsive means will gradually increaseuntil the energization of the current responsive means is sumcient toactuate the shorting means regardless of the failure of the motor speedto increase to a predetermined value.

11. In an automatic starter for electric motors having an armature. thecombination of a starting resistance arranged to be connected in serieswith the armature, a current controlled switch having a definite timelimit delay in closing after energization of the motor for shunting outthe starting resistance, the said switch including a coil for operatingthe switch when sufiiciently energized to overcome resistance to itsclosing, and current control means having a negative temperaturecoefilcient of resistance associated with the coil in such manner as togradually increase the current value through the coil until it reaches apredetermined maximum value after a definite lapse of time, the currentvalue necessary to sufficientl energize the coil to effect closing theswitch being less than said maximum value.

12. The combination with a motor armature of a starter resistance inseries with said armature, a shunting switch for the starter resistance,

means for closing the switch, holding means actuated by the startingcurrent resisting the closing of the switch when the current is above apredetermined value and a time lag means associated with the closingmeans to control operation of the closing means when the startingcurrent is sustained above said predetermined value for a lapse of time,the said time lag means operat ng to reduce the resistance of the closinmeans circuit until the current value therethrough is sufficient toenergize the closing means to a point where it is superior to theholding me ns and .thereupon close the shunting switch and shunt meansbeing so construct d and so operatin that the current value through thefirst solenoid will increase gradually as the armature current pers stsfor a time above sa d predetermined value until the energization of thefirst solenoid is sufficient to overcome the energization of the secondsolenoid and operate the shunting means to shunt out the startingresistance.

14. An automatic starter for an electric motor comprising a startingresistance, a normally open shunt ng switch arran ed to shunt out thestarting resistance, a holding coil connected in series with thestarting resistance and with the armature circuit to restrain theclosing of said switch, a solenoid for closing sa d shunting switch whensaid solenoid is sufficientlv energized and means in series with saidsolenoid to control the current flow through the solenoid whereby thecurrent value will gradually increase until the pull of said solenoid issuperior to that of the holding coil.

15. An automatic starter for electric motors comprising, a startingresistance, a switch for shunting out the starting resistance, a seriesconcomprising, a starting resistance, a normally open shunting outswitch arranged to short-circuit at least a part of said startingresistance, a holding coil responsive to the starting current forresisting the closing 01' said switch, a closing coil connectable inshunt with the motor armature for actuating the switch to its closedposition, and

a time lag means associated with the closing coil and its shuntconnection whereby the energizing current through said closing coil willin--' crease sufliciently to eiiect the closing of the switch ii. itdoes not close within a time interval after starting the motor.

17. An automatic starter for electric motors comprising, a startingresistance connectable in series with the armature of said motors,switching means for shunting said starting resistance, a control coilresponsive to the starting current of the armature of the connectedmotor to res st the operation of the switching means, a second controlcoil responsive to the counter E. M. F. of the connected motor tooperate the switching means to shunt the starting resistance, and meansassociated with the second control coil to assure sufiicient currentthrough said second coil to eiIect operation of the shunting switchafter a lapse of t me after starting the motor.

18. In an automatic starter for electric motors compr sing, a startingresistance and a switch adapted to shunt out at least a part of the strting resistance, and a current responsive coil with an energizingcircuit to operate the switch to its shunt ng position, the combinationwith the said coil 01' means to effect a current increase throu h saidcoil whereby the current will be made sufficient for the coil toovercome resistance to the operation of the switch.

19. In an automatic starter for electric motors compris ng a startingresistance and a shunting switch to shunt out at least a art of theresistance and a holdout coil res onsive to the start ng current throu hthe starting res stance ur ing said switch to maintain its non-shuntingposition and a second coil connected in shunt to a source of current oos n the holdout c l and operating the swi ch to its shunting position,the combination with the said second coil of control means whereby theeneraization. oi the second coil is automatic lly and graduallyincreased until the pull of the second coil is superior to that of theholdout coil.

20. In an automatic starter for electric motors comprising a startingresistance and a shunting switch to shunt out at least a part of theresistance and a holdout coil responsive to the starting current throughthe starting resistance urging said switch to maintain its non-shuntingposition and a second coil connected in shunt to a source of currentopposing the holdout coil and operating the switch to its shuntingposition, the combination with the said second coil of control meanswhereby the energization of the second coil is automatically andgradually increased until the pull of the second coil is superior tothat of the holdout coil, and means associated with the shunting switchand operated thereby 12 to shunt the control means when the startingresistance has been shunted.

21. In an automatic starter for electric motors comprising, a startingresistance and a switch adapted to shunt out at least a part of thestarting resistance, and a current responsive coil with an energizingcircuit to operate the switch to its shunting position, the combinationwith the said coil oi means to eiiect a current increase through saidcoil whereby the current will be made suflicient for the coil toovercome resistance to the operation of the switch, and means associatedwith the said switch and operated thereby to shuntout the said meansupon the closing of said switch.

22. An automatic starter for electric motors comprising, a startingresistance, a switch ior shunting out the starting resistance, a seriesconnected holding coil resisting the closing of the switch, a shuntconnected coil for closing the switch and a current responsiveresistance element connected in series with said shunt coil whereby thecurrent through the shunt coil will automatically increase when theshunt coil fails to close the switch after a lapse of time, and means toshunt the current responsive resistance element after the switch hasshunted the starting resistance.

23. In an automatic starter for electric motors comprising, a startingresistance and a switch adapted to shunt out at least a part of thestarting resistance, and a current responsive shunt connected coil toactuate the switch to its shunting position and connected to anenergizing circuit, the combination with the said coil of means having anegative temperature coefficient of resistance to eflect an increase ofcurrent through said coil whereby the current will be made suiiicientfor the coil to overcome resistance to the operation of the switch andmeans to shunt the said means after it has effected said currentincrease.

24. In an automatic starter for electric motors comprising, a startingresistance and a switch adapted to shunt out at least a part of thestarting resistance, and a current responsive coil to actuate the switchto its shunting position and connected to an energizing circuit, thecombination with the said coil of self-heating means having a negativecoefllcient of resistance to eiIect an increase of current flow throughthe coil alter a time lag whereby the current will be made suiflcientfor the coil to overcome resistance to the operation of the switch, andmeans to shunt the said means after it has ellected said currentincrease.

25. An automatic starter for an electric motor having an armature,comprising, a starting resistance, switch means for shunting thestarting resistance, the said switch means including current responsivemeans to operate the switch means, control means associated with thecurrent responsive means and having a negative coethcient of resistancewhereby the current through the current responsive means will graduallyincrease as the temperature of the control means increases until thecurrent is sufiicient to energize the current responsive meanssuilicient to operate the shunting means and other current responsivemeans positioned adjacent the control means to gradually heat thecontrol means to gradually reduce its resistance.

26. An automatic starter for an electric motor having an armature,comprisin a starting resistance, arranged to radiate heat and prevent arush of starting current through the motor armature, a switch forshunting the starting resistance, the said switch including currentresponsive means to operate the switch to its closed position, controlmeans having a negative coefficient of resistance associated with thecurrent responsive means to efifect a gradual increase of currentthrough said current responsive means until sufficient to efiectoperation of the switch to shunt out at least a portion of theresistance, the control means positioned adjacent the startingresistance to be affected by the heat radiated therefrom and therebyeffect a, decrease in its resistance and a corresponding increase incurrent flow through the current responsive means.

27. In an automatic starter for electric motors comprising a startingresistance and a switch adapted to shunt out at least a part of thestarting resistance and a current responsive coil to 29 actuate theswitch to its shunting position and connected to an energizing circuit,the combination with the said coil of control means having a negativecoefficient of resistance, current responsive means to gradually raisethe temperature of .the control means whereby the resistance i4 of thecontrol means will gradually decrease and the flow of current throughthe control means increase to effect operation of the switch and meansto shunt the control means upon operation of the switch to its shuntingposition.

EDWARD P. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,149,150 Steen Aug, 3, 19151,325,048 Simon Dec. 16, 1919 1,728,551, Jennings Sept, 17, 19291,516,646 Roseby Nov. 25, 1924 2,123,063 Peters July 5 1938 2,185,130Morrill et a1. Dec. 2c, 1939 1,136,312 Cartwright Apr. 20, 19151,691,735 Oberschmidt Nov. 13, 1928 FOREIGN PATENTS Number Gountry Date1 440,392 German Feb. '7, 1927

